Macromolecular resolution of fossilized muscle tissue from an elopomorph fish

Abstract

THE Santana Formation (Lower Cretaceous, Aptian/Lower Albian) of Ceara, Brazil, contains many exceptionally preserved fish fossils within carbonate concretions1,2. These concretions formed before compaction of the sediment and nucleated around carcasses of fish killed in mass-mortality events. Some concretions may contain several fish, preserved in three dimensions with fully articulated skeletons1. A few specimens contain calcium phosphate in the form of cryptocrystalline hydroxyapatite. This occurs as coatings on bones and as a replacement of tissues. Samples of mineralized soft tissues can easily be liberated from the concretions by immersion in 10% acetic acid3. Of several mineral phases often preserving soft tissues, calcium phosphate and silica probably offer the greatest resolution of detail4. Fossilized soft tissues are most frequently found in fishes, although in the Santana Formation pterosaur wing membrane5 and the cuticles of arthropods6,7 have been reported. I report here the study of striated muscle tissue from a fossil elopomorph fish8 from this formation, in which subcellular ultrastructural features are distinguishable. The exceptional degree of preservation of the specimen raises interesting questions about the mechanism of fossilization.